This invention relates to an electron beam exposure apparatus, more specifically to an electron beam exposure apparatus in which a deflected electron beam is projected on a workpiece in parallel with the optical axis of the apparatus.
In drawing a high-accuracy desired pattern on a workpiece by using an electron beam exposure apparatus, it is desired that an electron beam should be applied to the workpiece at right angles thereto. Otherwise it is impossible to draw a high-accuracy pattern since the workpiece has an uneven surface. Recently, a system has been proposed in which a deflecting device is interposed between two mask plates each having an aperture and the size of the electron beam is allowed to be made variable. In this system the electron beam can be projected as a spot having a shape corresponding to the shape of the aperture on a plane perpendicular to the optical axis, but the electron beam is, if deflected aslant, projected on such plane as a spot having a distorted shape. Therefore, it is necessary to project the electron beam on the workpiece always in parallel with the optical axis. Thereupon, according to the conventional method, the electron beam applied to the workpiece, even during deflection, is paralleled with the optical axis of the apparatus by using a telecentric lens system for the object lens, whereby the electron beam is applied at right angles to the workpiece disposed at right angles to the optical axis. This telecentric lens system, however, is special and very expensive. The diameter of the aperture of the telecentric lens is required to be equal to the sum of the deflection width of the electron beam and the numerical aperture (NA) of a projection lens. In this case, the exposure current is applied only at a value determined by NA, whereas the aberration is in proportion to the cube of the diameter of the aperture, that is, the deflection width plus NA. Consequently, the exposure current is small and the aberration is substantial, which is not very practical.